1. Field of the Invention
Example embodiments generally relate to a fixing device and an image forming apparatus, for example, for efficiently fixing a toner image on a recording medium using a rotatable fixing member.
2. Description of the Related Art
Image forming apparatuses, such as copiers, facsimile machines, printers, and multifunction devices having at least one of copying, printing, scanning, and facsimile functions, typically form a toner image on a recording medium (e.g., a sheet) based on image data using electrophotography.
For example, when an electrostatic latent image is formed on a surface of a photoconductor, serving as an image carrier, a development device develops the electrostatic latent image with a developer (e.g., toner) into a visible toner image. After a transfer device transfers the toner image onto a sheet, the toner image is fixed on the sheet by heat and pressure applied by a fixing device. Then, the sheet is discharged to the outside of the image forming apparatus via a discharge path.
FIGS. 1A and 1B illustrate one example of a related-art fixing device 900R. Left and right side plates 97A and 97B are vertically provided on a bottom plate 97C, as illustrated in FIG. 1B, and support a fixing roller 11R, a heating roller 14R, and a pressing roller 13R, respectively, as illustrated in FIG. 1A. A fixing belt 12R is wrapped around the fixing roller 11R and the heating roller 14R under an appropriate amount of tension supplied by a tension roller 15AR. The side plates 97A and 97B are reinforced by the bottom plate 97C, stays, and the like, so as to keep the respective rollers parallel to each other.
Since the fixing device 900R is detachably attached to the image forming apparatus, positioning members 98A and 98B engage a supporting member of the image forming apparatus so that the fixing device 900R is positioned in a predetermined place. The positioning members 98A and 98B are fixed to the side plates 97A and 97B by swaging and extend from a fixing cover 900C.
The right side plate 97A supports a drive input gear 99A with a support shaft, not shown, provided outside the fixing device 900R. The drive input gear 99A, serving as a drive input rotating body, receives a driving force transmitted from the outside (the image forming apparatus). A rotary shaft of the pressing roller 13R extends from the right side plate 97A. A pressing roller gear 99C is provided at one end of the rotary shaft of the pressing roller 13R in an axial direction of the rotary shaft.
Upon receipt of the driving force transmitted from the image forming apparatus, the drive input gear 99A rotates. When the rotation of the drive input gear 99A is transmitted to the pressing roller gear 99C via an idler gear 99B, the pressing roller 13R rotates. The fixing belt 12R is driven to rotate as the pressing roller 13R rotates.
When the fixing device 900R is attached to the image forming apparatus, a user moves the fixing device 900R in a direction perpendicular to shaft lines of the positioning members 98A and 98B, with a surface of the fixing device 900R on which a drawer connector 9A is provided facing toward the back of the image forming apparatus, so that the fixing device 900R is installed in a predetermined position of the image forming apparatus.
What is important here is that the shaft lines of the positioning members 98A and 98B are parallel to both a transfer roller and a registration roller provided in the image forming apparatus and the respective rollers (the fixing roller 11R and the pressing roller 13R) of the fixing device 900R, thereby properly conveying a sheet to a fixing nip formed between the fixing roller 11R and the pressing roller 13R of the fixing device 900R. If the fixing roller 11R and the pressing roller 13R are not positioned parallel to the transfer roller and a registration roller of the image forming apparatus, the sheet is fed unevenly to the feeding device 900R and bent or folded, thereby generating a crease or a difference in scale between left- and right-side images.
FIG. 2A is a sectional view of the fixing device 900R. When the drive input gear 99A receives,a driving force f′ from a driving gear 200AR of the image forming apparatus, one part of the force f′ is transmitted to the right side plate 97A depicted in FIG. 1B via the support shaft of the drive input gear 99A to lift up the whole fixing device 900R. When this occurs, since the fixing device 900R is supported by the image forming apparatus with the positioning member 98A, a rotational moment m′ is generated around the positioning member 98A due to the lifting force, as illustrated in FIG. 2B. Since the fixing device 900R receives the rotational moment m′, the right side plate 97A is twisted and deformed, causing the fixing roller 11R supporting the fixing belt 12R to lose its parallel position with respect to the pressing roller 13R opposing the fixing belt 12R. As a result, the fixing belt 12R may shift from a predetermined position in an axial direction of the fixing roller 11R, thereby generating a crease in the sheet.
In order to prevent such shift of a fixing belt, another related-art fixing device includes a supporting roller of the fixing belt to control shifting of the fixing belt. However, the fixing device requires a fixing belt position detector and a component for moving the support roller, thereby increasing both costs and size of the fixing device. In addition, such supporting roller cannot be used for a surf-fixing device in which no tension is applied to a fixing belt. FIG. 3 is a schematic view of a surf-fixing device 300 illustrating a structure thereof. The surf-fixing device 300 includes a fixing belt 32, a pressing roller 33, a ceramic heater 32H, a holder 32A, and a stay 32B. The fixing belt 32 is supported by one shaft, not shown, so that the fixing belt 32 easily loses its parallel position with respect to the pressing roller 33, thereby shifting from a predetermined position.
Accordingly, there is a need for a technology capable of keeping the respective rollers of a fixing device parallel to each other as well as to conveyance rollers of an image forming apparatus so as to prevent a shift of a fixing belt in an axial direction of the rollers.